Why Does Asynchronous Remote Replication Site Recovery Need Multiple Synchronization Operations?

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Multiple synchronization operations help minimize the write delay between the primary LUN and the secondary LUN. In addition, multiple synchronization operations are performed at short intervals. In this case, if you stop services and initiate data synchronization again, incremental data can be quickly synchronized before new write I/Os arrive. This prevents data loss and minimizes the downtime.

Other related questions:
What Is the Difference Between Synchronous Remote Replication and Asynchronous Remote Replication
Both synchronous remote replication and asynchronous remote replication can be used in disaster recovery solutions implemented by storage systems to back up data remotely. However, they are implemented in different ways and applicable to different service scenarios. Implementation modes are describes as follows: ? Synchronous remote replication: When a host writes data to the primary LUN, a write request is also sent to the secondary LUN. After both LUNs return a response indicating a successful I/O write, the primary storage system sends the host a response indicating a successful I/O write, implementing real-time data synchronization between the primary LUN and the secondary LUN. ? Asynchronous remote replication: When writing data to the primary LUN, the primary storage system records the changed data. After the primary LUN returns a response indicating a successful write, the primary storage system sends the host a response indicating a successful write. Then, data synchronization is triggered by a user manually or by the system based on user-defined trigger conditions to ensure data consistency between the primary LUN and the secondary LUN. Service scenarios are described as follows: ? Synchronous remote replication requires high bandwidth and low data latency. Therefore, synchronous remote replication is typically used in disaster recovery scenarios where the primary and secondary storage systems are adjacent to each other, such as the intra-city data backup and disaster recovery scenario. ? Asynchronous remote replication is not demanding on bandwidth and data latency. Therefore, asynchronous remote replication is applicable to disaster recovery scenarios where the primary and secondary storage systems are far away from each other or the network bandwidth is limited.

Introduction to the asynchronous remote replication period
The asynchronous remote replication period is manually set during the creation of an asynchronous remote replication task. The period control policies include Manual, Timed wait when synchronization begins, and Timed wait when synchronization ends. For a file system, the period control policy can be set to Specify the time policy in addition to the preceding ones.

What is the relationship between NAS remote replication and SAN asynchronous remote replication?
The N8500 NAS remote replication is implemented based on SAN asynchronous remote replication. Each N8500 NAS remote replication pair corresponds to a consistency group of SAN asynchronous remote replication. If any resource in the consistency group of SAN asynchronous remote replication is faulty, the N8500 NAS remote replication become invalid as well. Then the storage unit will generate an alarm. You can rectify the fault according to the suggested actions in the alarm.

Why cannot the initial synchronization of the LUN-based remote replication synchronize the file storage pool information?
The creation sequence of an N8500 LUN-based remote replication is to create a remote replication relationship, start initial synchronization, and then create a file storage pool. Therefore, a file storage pool is created after the synchronization process. After initial synchronization, the secondary LUN does not have the file storage pool information, and an alarm, File storage pools for replication fail to be obtained, will be generated for a disaster recovery test. Therefore, if you want to perform a disaster recovery test, start an incremental synchronization to synchronize the file storage pool information of the primary LUN to the secondary LUN.

Introduction to recovery plan tests executed by the OceanStor ReplicationDirector
You can test a recovery plan to verify the availability of the data replicated to the disaster recovery site. During a test, the disaster recovery site generates test data using snapshots, which does not have any impact on the production site. After the test is complete, the test environment must be cleaned up. Before a failover or planned migration, at least one recovery plan test must be executed successfully. The test can be performed only in the disaster recovery management system at the disaster recovery site.

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